1. Field of the Invention
The present invention relates to a technology that is well adaptable to an electric storage device having incorporated therein an ion source.
2. Description of the Related Arts
A lithium ion secondary battery or a lithium ion capacitor has been proposed as an electric storage device that is mounted on an electric vehicle, hybrid vehicle, or the like. There has also been proposed an electric storage device in which a metal lithium foil serving as an ion source is incorporated in the electric storage device so as to bring a negative electrode and the metal lithium foil into electrochemical contact with each other in order to enhance an energy density of the electric storage device. By this configuration, lithium ions can be doped into the negative electrode from the metal lithium foil. Therefore, the potential of the negative electrode can be lowered to increase a cell voltage. As a result, the energy density of the electric storage device can be enhanced (see JP-A-2006-286919).
In order to incorporate the metal lithium foil in the electric storage device, it is general that the metal lithium foil is cut into a predetermined shape, and then the resultant is adhered onto a lithium-electrode current collector. However, it is very difficult to cut only a soft thin metal lithium foil. In view of this, there has been proposed a manufacturing method in which a lithium-electrode current collector drawn out from a roll and the metal lithium foil are press bonded so as to be integral with each other, and then the lithium-electrode current collector and the metal lithium foil are both cut, in order to facilitate the cutting operation of the metal lithium foil (e.g., see JP-A-2007-173615).
However, in order to incorporate the metal lithium foil into the electric storage device, not only the operation of adhering the cut metal lithium foil onto the lithium-electrode current collector is needed, but also the operation of welding the lithium-electrode current collector having the metal lithium foil adhered thereon onto the negative-electrode current collector is needed. In the welding operation, the thin soft metal lithium foil might be damaged, which leads to increased cost of the electric storage device. The metal lithium foil is easy to react with water content. Therefore, the operation of welding the lithium-electrode current collector onto the negative-electrode current collector should be done in a dry room or in an argon box. Thus, the welding operation is troublesome, which also leads to the increased cost of the electric storage device.